The present invention relates to an cam-using electronic control sewing machine for selecting a stitch pattern or patterns by driving a pulse motor and for automatically sewing a button hole or holes.
It is known in the prior art that this kind of stitch pattern selecting machine uses a servomotor for driving a cam-follower of the stitch pattern cams (see the Japanese public inspection laid open Pat. No. 19250/1978).
Because the stitch pattern selecting machine, however, uses the servomotor, the difference voltage between the present position and the selected position of the cam-follower is detected by a potentiometer and is supplied to the servomotor as a feedback signal. Therefore, when the cam-follower comes near to a selected position, the difference voltage becomes small and consequently the servomotor is not smoothly driven and the cam-follower is not exactly moved to the selected position.
Therefore, in the prior art, for solving the inaccuracy of the positioning of the cam-follower, a projecting pin attached to the opposite side of the cam-follower is inserted between respective two teeth of a toothed bar or into the window of the position correcting board corresponding to the stitch pattern cams.
Also, the other stitch pattern selecting machine in the prior art uses an electric motor for driving a cam-follower of the stitch pattern cams (Japanese public inspection laid open Pat. No. 159047/1979).
This usual machine comprises a detector for detecting the position of the cam-follower, a counter for counting electric pulse signals generated by the detector and a comparator for comparing coded signals from an operated switch of the selection switches with the output signals of the counter. The electric motor is stopped by the accord signal from the comparator.
In the usual machine, the position signals of the cam-follower are fed back and are compared with the siganls of the selected switch of the selection switches and the electric motor is stopped by the accord siganl from the comparator. Therefore, the cams, the switches and the comparator for detecting the cam-follower are used and thus the composition of the usual machine is complex.
Also, usual automatic button hole stitch sewing device comprises a plurality of pattern cams for sewing each step of button hole stitches and means for memorizing the number of stitches by an electronic control device (Japanese public inspection laid open Pat. No. 12680/1983).
In the usual automatic button hole stitch sewing device, however, because left line tack stitches and right line tack stitches must be designated by pushing switches, the sewing operation is complex.